1. Technical Field
The present invention relates generally to a diesel fuel composition containing a soot dispersant additive which is a grafted and derivatized low molecular weight copolymer of ethylene and at least one C3-C10 alpha monoolefin.
2. Description of the Related Art
The diesel engine is a common powerplant choice when economic factors such as fuel economy, durability and efficiency are prime considerations. To extract the greatest utility from a diesel engine, lubricant drain intervals are often extended in commercial applications to minimize unproductive downtime for maintenance. The limit of a diesel engine's drain interval length is often related to the level of exhaust particulates that accumulate in the lubricant. While lubricant additive formulations are designed to accept and manage certain amounts of soot, when that capability is depleted, soot particle agglomeration may cause a sudden, significant viscosity increase, aggravate engine wear, handicap low temperature operation, form harmful sludge and result in a fuel economy penalty. Exhaust gas recirculation (EGR) exacerbates soot accumulation and further taxes the oil's performance over time.
A unique approach to extending the service life of a diesel engine lubricant and, consequently, increasing the economy of engine operation, is to introduce a predetermined amount of soot dispersant additive into the fuel with the object of having such additive become incorporated into the lubricant during engine operation in an amount and at a rate which will make up at least in part for the normal and expected consumption of soot dispersant additive that had previously been added directly to the lubricant in accordance with known and conventional practice.
However, the inherent nature of diesel engine operation raises several technical hurdles to a successful realization of this approach. In order to become incorporated into the lubricant, soot dispersant additive present in the fuel must pass through the combustion chamber with its chemical integrity intact and accumulate in the crankcase where it can then replenish the soot dispersant additive that has been consumed. The major technical problem to overcome is that the very nature of a diesel engine minimizes the opportunity for typical fuel additives to reach the cylinder wall. Specifically, the exposure of a compression ignition engine's cylinder to diesel fuel prior to combustion is very short relative to those timeframes encountered in gasoline engines. Moreover, in diesel engine operation, the fuel spray is directed at the piston, not the cylinder wall as in gasoline engine operation. Therefore, diesel fuel additive candidates must possess a different set of physical and chemical qualities to reach the oil coated cylinder surfaces than those requires in gasoline engine applications.
Possibly because of the aforementioned technical challenges, it is believed that the practice up until now has been one of directly adding soot dispersant additive solely to the diesel engine lubricant and not to the fuel.
Accordingly, there is a need for a diesel fuel which contains a soot dispersant additive capable of passing intact into the diesel lubricant so as to continuously replenish dispersant additive as the latter is consumed during the normal course of engine operation.